Hydraulic percussion rock drills have been developed which provide for substantially all drill functions, except drill hole flushing, to be performed by hydraulic pressure fluid. Drill percussion mechanisms as well as drill stem rotation motors and feed motors are desirably hydraulically powered for greater efficiency for deriving more power from a smaller machine than has been possible with pneumatic powered drills. The development of hydraulic percussion drills has, however, resulted in more complex control circuits due to the fact that hydraulic fluid return lines must be provided and, heretofore, it has been deemed desirable to use multiple pumps for supplying pressure fluid to the various motors on the drill and the associated feed mechanism. Moreover, the more powerful hydraulic drills have made it more desirable that the relationship of feed force, drill stem rotation effort, and percussive energy should be controlled to provide optimum drilling rates. However, the automatic control of each of these functions becomes difficult and requires expensive components when multiple hydraulic circuits are used.
The development of hydraulic percussion drills has further resulted in the desire to provide even greater drilling rates by the use of controls to vary the percussion blow intensity and blow frequency to suit the particular drilling conditions. Improvements in such controls as well as the provision of a hydraulic percussion drill powered by a constant power hydraulic source is the subject of the invention disclosed and claimed in U.S. Pat. No. 3,995,700 assigned to the assignee of the present invention.
In the further development of percussion drills having variable percussion blow frequency controls it has been determined that it is desirable to vary blow frequency and blow intensity in relation to resistance to forward feeding of the drill and also in relation to resistance to rotation of the drill stem and bit. Moreover, it is considered desirable that on retraction of the drill from the work that blow intensity be decreased to prevent possible damage to the percussion mechanism.
The problems associated with prior control systems for hydraulic drills as well as certain improvements foreseen as being desirable in the art of hydraulic percussion drills have been dealt with in developing the invention disclosed and claimed herein.